The invention described here is related to the clinical use and automatic control of a blood pump in the human circulation system. In general there are various physiological parameters that are of interest to clinicians that care for patients that are undergoing circulatory assistance from a mechanical device. Many of these same parameters may be desirable to be obtained for use in an automatic cardiac output controller to be used in combination with the mechanical pump. Examples of physiological parameters that could be used include flow through the pump and pressures at the inflow and the outflow of the pump.
One method to obtain a flow rate through a blood pump is to place sensors directly in the flow path. However this approach is saddled with reliability issues of sensors directly exposed to blood, in addition to wires and cable associated with such sensors. Sensor placement directly in the blood flow is undesirable because the blood can cause malfunction of the sensor due to contamination of the sensing element and wiring, or due to blood clotting around the sensing element resulting in lost sensitivity of the sensor. The sensor itself can also damage the blood cells themselves creating blood clots.
Some physiological controllers may rely on measuring pressure to determine desired physiological parameters. However, these sensors are difficult to implement within a patient, lack the required sensitivity, and are quite expensive.
Some physiological controllers adjust the speed of the pump based upon a comparison to failure levels of the patient's heart. U.S. Pat. Nos. 5,888,242 and 6,066,086 to Antaki et al. teach an automatic speed control system which continually adjusts the speed of an implanted cardiac assist blood pump to an optimum level for the varying physiological needs of the patient. It does this by periodically iteratively incrementing the speed set point of the pump. When the system detects the imminence of a ventricular collapse at the end of systole, it decrements the speed set point by a predetermined safety margin. These attempts at avoiding the direct sensor placement in the blood suffer some drawbacks. For example, a speed set point of the heart pump that is set at a predetermined point compared to ventricular collapse may not be the optimum speed for a particular patient. Additionally, incrementing the speed set point of a heart pump toward an imminent ventricular collapse comparison point may be dangerous.
Additionally, choosing the speed set point of a heart pump by arbitrarily setting the speed a predetermined amount away from a failure point does not provide any diagnostic feedback to the physician monitoring the patient.
Thus, it would be an advancement in the art to provide a physiological heart pump or cardiac output controller that did not need blood flow sensors for daily operation. It would be an additional advancement in the art to provide such a cardiac output controller that better tracked the optimum pump performance based on the patient's physiological makeup. It would be a further advancement in the art if the cardiac output controller were more cost-effective. It would be yet another advancement in the art if the cardiac output controller could provide diagnostic feedback.
Such a cardiac output controller, and method of operating same, in accordance with the present invention is disclosed and claimed herein.